In the medical field, where beneficial agents are collected, processed and stored in containers, transported, and ultimately delivered through tubes by infusion to patients to achieve therapeutic effects, materials which are used to fabricate the containers must have a unique combination of properties. For example, in order to visually inspect solutions for particulate contaminants, the container must be optically transparent. To infuse a solution from a container by collapsing the container walls, without introducing air into the container, the material which forms the walls must be sufficiently flexible. The material must be functional over a wide range of temperatures. The material must function at low temperatures by maintaining its flexibility and toughness because some solutions, for example, certain pre-mixed drug solutions are stored and transported in containers at temperatures such as −25° C. to −30° C. to minimize the drug degradation. The material must also be functional at high temperatures to withstand the heat of sterilization; a process which most medical packages and nutritional products are subjected to prior to shipment. The sterilization process usually includes exposing the container to steam at temperatures typically 121° C. and at elevated pressures. Thus, the material needs to withstand the temperature and pressures without significant distortions (“heat distortion resistance”).
For ease of manufacture into useful articles, it is desirable that the material be sealable using radio frequency (“RF”) generally at about 27.12 MHZ. Therefore, the material should possess sufficient dielectric loss properties to convert the RF energy to thermal energy. A further requirement is to minimize the environmental impact upon the disposal of the article fabricated from the material after its intended use. For those articles that are disposed of in landfills, it is desirable to use as little material as possible and avoid the incorporation of low molecular weight leachable components to construct the article. Thus, the material should be light weight and have good mechanical strength. Further benefits are realized by using a material which may be recycled by thermoplastically reprocessing the post-consumer article into other useful articles.
For those containers that are disposed of through incineration, it is necessary to use a material that helps to eliminate the dangers of biological hazards, and to minimize or eliminate entirely the formation of inorganic acids which are environmentally harmful, irritating, and corrosive, or other products which are harmful, irritating, or otherwise objectionable upon incineration.
It is also desirable that the material be free from or have a low content of low molecular weight additives such as plasticizers, stabilizers and the like which could be released into the medications or biological fluids or tissues thereby causing danger to patients using such devices or are contaminating such substances being stored or processed in such devices. For containers which hold solutions for transfusion, such contamination could make its way into the transfusion pathway and into the patient causing injury or death to the patient.
Traditional flexible polyvinyl chloride materials meets a number of, and in some cases, most of the above-mentioned requirements. Polyvinyl chloride (“PVC”) also offers the distinct advantage of being one of the most cost effective materials for constructing devices which meet the above requirements. However, PVC may generate objectionable amounts of hydrogen chloride (or hydrochloric acid when contacted with water) upon incineration, causing corrosion of the incinerator. PVC sometimes contains plasticizers which may leach into drugs or biological fluids or tissues that come in contact with PVC formulations. Thus, many materials have been devised to replace PVC. However, most alternate materials are too expensive to implement and still do not meet all of the above requirements.
There have been many attempts to develop a film material to replace PVC, but most attempts have been unsuccessful for one reason or another. For example, in U.S. Pat. No. 4,966,795, which discloses multilayer film compositions capable of withstanding the steam sterilization, cannot be welded by radio frequency dielectric heating thus cannot be assembled by this rapid, low costs, reliable and practical process. European Application No. EP 0 310 143 A1 discloses multilayer films that meet most of the requirements, and can be RF welded. However, components of the disclosed film are cross-linked by radiation and, therefore, cannot be recycled by the standard thermoplastic processing methods. In addition, due to the irradiation step, appreciable amounts of acetic acid is liberated and trapped in the material. Upon steam sterilization, the acetic acid migrates into the packaging contents as a contaminant and by altering the pH of the contents acts as a potential chemical reactant to the contents or as a catalyst to the degradation of the contents.
U.S. Pat. No. 5,998,019, which is owned by the same assignee of the present invention, discloses multi-layered polymer structures that solve many, if not all, of the foregoing problems. However, one problem with the structures of the '019 patent is that the internal solution contact layer of those structures sticks to either itself or to other similar structures (such as other films or when formed into a container) after the autoclave sterilization process. The internal solution contact layer of the '019 patent is either an RF sealable layer or a blend of two polyolefins and a compatibilizing agent of a styrene and hydrocarbon block copolymer. The specific composition of the RF sealable layer is disclosed therein and is also the subject of U.S. Pat. Nos. 5,849,843; 5,854,347 and 5,686,527, which are owned by the present assignee and are incorporated by reference.
U.S. Pat. No. 6,083,587, also owned by the present assignee, provides a multilayer structure where the internal solution contact layer can be a polyolefin selected from the homopolymers and copolymers of alpha-olefins having about 2 to about 20 carbons. However, the '587 patent does not disclose a structure wherein an internal, non-solution contact layer is RF sealable layer or comprised of an RF susceptible polymer.
The main objective of the present invention is the creation of thermoplastic materials which are, overall, superior to those materials, of which we are aware, which have been heretofore known to the art or have been commercially used or marketed. The properties of such materials includes flexibility, extensibility, and strain recoverability, not just at room temperatures, but through a wide range of ambient and refrigerated temperatures. The material should be sufficiently optically transparent for visual inspection, and steam sterilizable at temperatures up to 121° C. The material should be capable of being subjected to significant strains without exhibiting strain whitening, which can indicate a physical and a cosmetic defect. A further objective is that the material be capable of assembly by the RF methods.
Another objective is that the material be substantially free of low molecular weight leachable additives, and be capable of safe disposal by incineration without the generation of significant amounts of corrosive inorganic acids. Another objective is that the material be recyclable by standard thermoplastic processing methods after use. It is also desirable that the material incorporate reground scrap material recovered during the manufacturing process to save material costs and reduce manufacturing waste. It is also desirable that the material not have its RF sealable layer able to contact itself of that of another film, minimizing the film from sticking to itself or to other films during, or subsequent to, the autoclave process. It is also desirable that the material not be oriented, as oriented films may shrink when subjected to heat. Finally, the material should serve as a cost effective alternative to various PVC formulations currently being used for medical devices.
When more than one polymer is blended to form an alloying composition, it is difficult to achieve all of the above objectives simultaneously. For example, in most instances alloy composition may scatter light; thus, they fail to meet the optical clarity objective. The light scattering intensity (measured by haze) depends on the domain size of components in the micrometer (μm) range, and the proximity of the refractive indices of the components. As a general rule, the selection of components that can be satisfactorily processed into very small domain sizes, and yet with a minimum of refractive index mismatches, is a difficult task. Also, film structures heretofore known usually contain stearates or fatty acids in the solution-contact layer of the structure, thereby permitting those undesirable components to leach into the solution in contact with the film structure.
The present invention is provided to solve these and other problems.